LR Question 15 Explanation, by LSATHacks
QUESTION TEXT: Astronomer: In most cases in which a planet has been…
QUESTION TYPE: Strengthen
CONCLUSION: Some planets with oval orbits around a distant star probably developed those orbits as a results of a encounter with other planets orbiting the same stars.
REASONING: Some comets orbiting our sun had encounters with planets and fell into oval orbits.
ANALYSIS: The author is saying that encounters with planets caused the oval orbits. I couldn’t prephrase anything here. So I just went into the answers remembering “they are saying that two planets had an encounter, leading to oval orbits.”
If you are precise about what you know, you can spot the right answer more easily. That phrasing above let me find the answer quickly.
A couple other notes:
- The fact that some planets around our sun have circular orbits isn’t too relevant. All it shows is that not all planets have oval orbits.
- The author didn’t say that every encounter causes oval orbits. They just said that encounters could cause oval orbits.
Not every cause is a 100% sufficient cause that works every time. So an encounter + no oval orbit isn’t evidence against the argument.
Note also that the argument is not saying that only encounters with other planets can cause oval orbits. The author just says “some of the planets” were, which leaves open the possibility that there are other causes.
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- Who cares which planet is affected more? The argument only requires that it’s possible for one planet to affect another planet enough that it takes an oval orbit.
- So? The author didn’t say that planetary encounters always produce oval orbits. A close encounter in the solar system + lack of an oval orbit wouldn’t harm the argument.
Also the argument didn’t say that all planets in the solar system have circular orbits. It just said several do. So if there are oval planets in the solar system too then this answer has even less impact.
- CORRECT. The author said that planetary encounters cause some oval orbits. To have an encounter, you need more than one planet. So this answer strengthens the argument by showing that collisions were indeed possible.
- Careful. This might have been right if it said “a close encounter with a planet”. But it doesn’t say that. It says “with some other object”. Those other objects might not be planets.
This answer is too vague to impact the argument. - This weakens the argument. The author is trying to argue that a collision with another planet caused the oval orbits of planets. Another planet is “an other object large enough to affect the planet’s orbit.”
So the argument requires there to be other objects large enough to affect orbits (i.e. other planets).
More Resources for Strengthen Questions
- Intro Course lesson: This intro course lesson covers Strengthen questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers strengthen questions.
I chose A over C because I misread it relative to stimulus, mainly due to the idea of planets being “close” to eachother in encounters (in and of itself too ambiguous to probably be useful, would love to know a tutors thought there).
Reviewing I think explanation for why A is wrong isn’t really getting at the core of why it’s wrong: I now think it’s wrong because it leaves amibiguity on if its a planet or another large object that impacts the orbit.
C is simply less ambiguous, although leaves room to question if planets would indeed be close enoguh to affect the orbit.
I can see why “close encounters” may seem vague, but further specification is not needed in the LSAT context. The test is not delving into astronomy details, and it would not be necessary information to understand and answer the question.
I don’t believe there’s ambiguity regarding what affects the orbit in answer A. The “two planets OR other large objects” does not imply ambiguity about the cause; “or” is an indicator that the sentence is referring to two possibilities.
#1: Two planets close encounter → smaller more affected. This might be true, but it doesn’t prove that planets in oval orbits were influenced by other planets.
#2: Large objects close encounter (either with a planet or another object) → smaller more affected. We know this is true for comets. Still doesn’t help strengthen our argument about planets.
Regarding answer C, whether or not they’re “close enough” is not necessary information. The argument only requires the possibility of close encounters, not that they occur every time. While it’s understandable to think about the specifics, the main point is that C supports the astronomer’s claim by showing that multiple planets orbit a distant star, making close encounters possible, thereby strengthening the argument.
Hope that helped! And apologies for the late response.
Just thought I’d add another reason that D is wrong:
Consider the sentence:
“However, many comets orbiting our sun have been thrown into oval orbits by close encounters with planets orbiting our sun.”
This sentence serves as an example of this proposed cause occurring in our system.
All that Answer Choice D does is specify that this is the case most of the time, in our system, the supporting example. Since the sentence above says “many” comets, and not any specifiers of probability, there is actually no presumption whether there is another potential cause of oval orbits in our system. Therefore, all that this Answer Choice actually does is introduce that there is a possibility that something else caused the oval orbit, which weakens.
Encounters are not supposed to mean collision here. It means they got close enough to be affected by the gravitational forces of large planets. Not that it matters but still.
Good catch! I fixed it.
Thanks for the explanation. I chose E because I actually thought choice E means that no other objects (other than planets orbiting the same stars) are large enough to affect the planet’s orbit. Thanks